This invention relates generally to a device for applying a release liner to an adhesive that is disposed on a substrate, and more particularly to an improved accumulator that regulates the tension in the release liner as the liner is being applied.
Automated gluing systems are routinely used to affect high-speed, repeatable application of adhesives to various substrates such that upon contact between the adhesive-containing substrate and another surface, a bond or seal is formed. Such systems are employed in deferred-use packaging, where a pressure-sensitive adhesive is covered with a release liner such that upon subsequent removal of the release liner and placement of the exposed adhesive in contact with a desired surface, the surface on which the adhesive is placed and the desired surface can be joined. In one form, the adhesive is integrated into a double-sided transfer tape that can be placed onto a substrate, where the side of the tape facing away from the substrate retains its layer of release liner to prevent the adhesive from being exposed until needed. While the transfer tape generally performs well, it is expensive and, due in part to its multiplicity of layers, very bulky. In another popular form, the adhesive is placed in a hot-melt liquid form onto a substrate, then covered with a layer of release liner. The hot melt approach is advantageous over the transfer tape approach because the lower bulk permits longer run-times between replenishment of the adhesive and release liner. In addition, the material costs are considerably lower than for transfer tape-based systems. Both the hot-melt approach and the transfer tape approach have been used extensively in the manufacture of paper and related products, such as corrugated cardboard sheet.
In a conventional gluing station utilizing the hot-melt approach, the sheet is fed adjacent an aligned valve and nozzle such that upon actuation of the valve, a stream of the adhesive is deposited onto the desired location on the sheet through the nozzle. Downstream of that, a release liner application station places a layer of release liner (such as a silicone-coated film or tape) on top of the adhesive to protect it. One shortcoming of existing release liner application stations is that the liner tape or film is pulled from a roll that exhibits inertial effects that can alternately place too much or too little tension on the release liner. In situations involving too much tension on the liner, the concomitant pulling produces a tendency in the liner to slide out of the desired position on the underlying adhesive. Similarly, in situations involving too little tension, the liner can become slack, such that when tension is restored, a snapping motion can ensue, enhancing the possibility of liner breakage, especially in situations where the liner is very thin in order to keep cost and bulk down. Accordingly, what is needed is a way to buffer the supply of release liner so that it can be applied intermittently and at low tension to a layer of adhesive disposed on a substrate.